The present application claims priority to Japanese Application No. P2000-059848 filed Mar. 6, 2000, which application is incorporated herein by reference to the extent permitted by law.
This invention relates to a solid electrolyte cell having a solid electrolyte.
In keeping up with the recent tendency to reduction in size and weight and popularity of portable type versions of an electronic equipment, such as a camera built-in Video T ape Recorder or a mobile information terminal, further size reduction with a higher energy density is demanded of a secondary cell as a power supply source for these electronic equipment.
The secondary cells for general use may be enumerated by an aqueous solution type lead accumulators or nickel-cadmium cells, and non-aqueous electrolyte solution cells. However, since these secondary cells use a liquid as an electrolyte, there is a risk of leakage of the internal solution which possibly affects ambient electronic parts. With this in mind, a solid electrolyte, that is an electronic solution in a solidified form, has been proposed.
In particular, a gelated solid electrolyte, obtained on impregnating a matrix polymer with a non-aqueous solvent, referred to below as a gel electrolyte, is now being researched briskly because its electrolytic solution phase represents a main path for the ion conduction and hence high-level ion conductivity corresponding to that of the electrolytic solution is felt to be promising
The non-aqueous electrolyte solution secondary cell, employing the gel electrolyte, is constructed as follows: A positive electrode active material, comprising e.g., LiCoO2 and graphite, is layered on a positive electrode current collector comprised of a thin aluminum sheet, to form a positive electrode. On the other hand, a negative electrode active material comprising e.g., carbon, coke or graphite, is formed on a positive electrode current collector comprised of a thin copper sheet, to form a negative electrode. A separator formed as a fine porous film of e.g., polypropylene or polyethylene is sandwiched between the negative and positive electrodes, while a gel electrolyte is charged into a space between the negative and positive electrodes and the separator to complete a element cell as a sandwiched structure. This element cell is hermetically sealed and accommodated in the interior of a sealing material comprised of a thin metal film, such as an aluminum foil, and plastic films, such as nylon, polyethylene, polypropylene and polyethylene terephthalate.
The non-aqueous solvent, used in the above-described non-aqueous electrolyte solution secondary cells, may be enumerated by, for example, carbonates or esters, such as ethylene carbonate, propylene carbonate, diethyl carbonate, xc3xa3-butyrolactone. These solvents are known to undergo deterioration in cell characteristics on repeated charging/discharging with the charging voltage exceeding 4V or on prolonged storage in charged state, as disclosed in Japanese Laying-Open Patent Publication Nos. H-4-332479 and H-337247. This deterioration in characteristics is appreciably ascribable to oxidative decomposition of the non-aqueous solvent under elevated voltage. Thus, for improving the performance of the high-capacity non-aqueous electrolyte solution cell of the order of 4V, it is imperative to improve characteristics of the non-aqueous solvent. Moreover, in a solid electrolyte cell employing the solid electrolyte as the electrolyte, measures for preventing oxidative decomposition of solid electrolyte components are felt to be desirable.
For preventing deterioration of cell characteristics due to oxidative decomposition of solid electrolyte components as described above, there has been proposed a cell containing a toluene component, as disclosed in e.g., the Japanese Laying-Open Patent Publication H-4-249870. There has also been proposed a method for adding a compoind coordinated in stability with respect to lithium ons, in order to prevent decomposition of the non-aqueous solvent on the surface of the negative electrode of carbon, as disclosed in the Japanese Laying-Open Patent Publication H-9-35746.
However, the above-described methods are insuffcient as means for preventing the cell performance from being deteriorated due to oxidative decomposition of solid electrolyte components, such that the cell performance is deteriorated with repetition of the charging/discharging cycles,
It is therefore an object of the present invention to provide a solid electrolyte cell in which oxidative decomposition of solid electrolyte components may be suppressed to maintain superior cell performance.
According to the present invention, there is provided a solid electrolyte cell including a positive electrode having a positive electrode current collector and a positive electrode active material, a negative electrode having a negative electrode current collector and a negative electrode active material, and a solid electrolyte comprised of an electrolyte salt dispersed in a matrix polymer. The solid electrolyte is arranged between the positive electrode and the negative electrode, and a diene compound is contained in at least one of the positive electrode, negative electrode and the solid electrolyte.
According to the present invention, as described above, a diene compound is contained in at least one of the positive electrode, negative electrode and the solid electrolyte to capture active oxygen to prevent oxidative decomposition of the electrolyte components. So, it is possible to suppress deterioration of the cell performance ascribable to oxidation of the electrolyte components to maintain superior cell performance.